A thermal expansion valve is an important component of a refrigerating system, and is one of four essential components of the refrigerating system, and the other three essential components include an evaporator, a compressor and a condenser. A main function of the thermal expansion valve is to control the valve opening by sensing a degree of superheat at an outlet end of the evaporator or an inlet end of the compressor in the refrigerating system, thereby adjusting a flow rate of the refrigerant and realizing the throttling and depressurizing of the system.
Referring to FIG. 1, FIG. 1 is a schematic view showing the structure of a typical thermal expansion valve in the prior art.
The thermal expansion valve includes a valve body 1′, and an upper end of the valve body 1′ is connected with an air box including an air box seat 2′4 and an air box cap 2′5. An inner chamber of the air box is separated into an upper chamber 2′2 and a lower chamber 2′3 by a diaphragm 2′1. As shown in FIG. 1, the upper chamber 2′2 is filled with a refrigerant and is connected to a thermo bulb 4′2 via capillary tubes 4′1. The thermo bulb 4′2 is used for sensing the degree of superheat of the refrigerant at the outlet end of the evaporator or the inlet end of the compressor to create a temperature pressure Pb in the upper chamber. The lower chamber 2′3 communicates with the outlet end of the evaporator via a balance pipe (not shown), and an evaporation pressure Po is created in the lower chamber 2′3.
Furthermore, as shown in FIG. 1, the inner chamber of the valve body 1′ is formed with a valve port 1′1 cooperated with a valve core 3′1. An upper end of the valve core 3′1 is connected with a transmission rod 3′2 which is connected to a transmission piece 3′3 located in the lower chamber. It is to be noted that, in the prior art, the valve core 3′1, the transmission rod 3′2, and a guide ball 3′4 described below are collectively referred to a valve core component, therefore the valve core component in the present prior art is formed by separated components. A guide ring 7′ is sleeved outside the valve core 3′1′, a chamber below the guide ring 7′ is a balance chamber 1′4, and a spring 6′ for supporting the valve core 3′1 is arranged in the balance chamber 1′4 and exerts an upward elastic force Pt on the valve core 3′1.
Taking the valve core 3′1 and the transmission rod 3′2 as objects for pressure analysis, the valve core 3′1 and the transmission rod 3′2 are both subjected to the upward elastic pressure Pt and a downward pushing force from the transmission piece 3′3. The pushing force is produced by the diaphragm 2′1 pushing the transmission piece 3′3, thus the pushing force is a force causing the diaphragm 2′1 to move downward, i.e., Pb−Po. When the valve core 3′1 is in a balanced state, Pb−Po=Pt, i.e., Pb=Po+Pt, if a temperature at the outlet end of the evaporator is too high, Pb is increased, which pushes the valve core 3′1 downwards, thereby increasing the flow of the refrigerant; and if the temperature at the outlet end of the evaporator is too low, Pb is decreased, which pushes the valve core 3′1 upward, thereby decreasing the flow of the refrigerant.
However, as shown in FIG. 1, during practical working, in addition to the above temperature pressure Pb, the evaporation pressure Po and the elastic pressure Pt from a spring, the valve core 3′1 may also be subjected to a pressure generated by the refrigerant in the first connecting chamber 1′2 to open the valve core 3′1 and a pressure generated by the refrigerant in the second connecting chamber 1′3 to close the valve core 3′1. A difference value between the two pressures generates a systematic pressure difference. For a valve with small capacity, or a low pressure refrigerating system, the affect on the valve core 3′1 caused by the systematic pressure difference may be ignored. However, for a valve with large capacity or a high pressure refrigerating system, the affect on the valve core 3′1 caused by the systematic pressure difference is significant, which may severely affect the adjusting accuracy of the valve core 3′1.
In view of this, as shown in FIG. 1, the valve core 3′1 is provided with a through hole 3′11 to communicate the first connecting chamber 1′2 with the balance chamber 1′4. A lower end of the through hole 3′11 is cooperated with a guide ball 3′4, and a gap is formed between the guide ball 3′4 and the through hole 3′11, such that pressures in the two chambers are equal, and a bearing area of a first pressure-bearing surface S′1 in the first connecting chamber 1′2 is equal to a bearing area of a second pressure-bearing surface S′2 in the balance chamber 1′4. Since the first pressure-bearing surface S′1 and the second pressure-bearing surface S′2 are subjected to pressures in opposite directions, pressures on the valve core 3′1 from the refrigerant in the first connecting chamber 1′2 are offset by each other. As shown in FIG. 2, a third pressure-bearing surface S′3 and a fourth pressure-bearing surface S′4 subjected to pressures in opposite directions are arranged in the second connecting chamber 1′3. Since the two pressure-bearing surfaces have the same bearing surface, pressures on the valve core 3′1 from the refrigerant in the second connecting chamber 1′3 are offset by each other. Therefore, whether the refrigerant flows from the first connecting chamber 1′2 to the second connecting chamber 1′3 or flows from the second connecting chamber 1′3 to the first connecting chamber 1′2, the systematic pressure difference is substantially equal to zero, thereby realizing a bidirectional balanced flow of the thermal expansion valve.
However, in the above prior art, as shown in FIG. 1, a first sealing member 8′1 is arranged between an upper end portion of the transmission rod 3′2 and the valve body 1′ to separate the first connecting chamber 1′2 from the lower chamber 2′3. A second sealing member 8′2 is arranged between the valve core 3′1 and the guide ring 7′ to separate the second connecting chamber 1′3 from the balance chamber 1′4. Since both the transmission rod 3′2 and the valve core 3′1 move along the axial direction, the above two seals are transmission seal and have the following disadvantages.
Firstly, the sealing performance of the transmission seal is not reliable. The leakage will be increased with the extension of the working life and the aging of rubber, which may increase the degree of superheat of the thermal expansion valve, and affect the reliability and accuracy of the thermal expansion valve.
Secondly, the transmission seal has a large frictional resistance, and the frictional resistance may be further increased with the extension of the working life and the aging of rubber, which may affect the sensitivity of the thermal expansion valve.
Thirdly, a high precision requirement is required for the cooperation between the valve body 1′ and the transmission rod 3′2 and the cooperation between the valve core 3′1 and the guide ring 7′, thus the valve body 3′1, the transmission rod 3′2, the valve core 3′1 and the guide ring 7′ are difficult to process. If the sealing between the valve body 1′ and the transmission rod 3′2 and the sealing between the valve core 3′1 and the guide ring 7′ are realized by a high precision cooperation seal instead of using sealing members, the valve body 1, the transmission rod 3′2, the valve core 3′1 and the guide ring 7′ will become more difficult to process.
Furthermore, the thermal expansion valve in the above prior art further has the following disadvantages.
Firstly, since the second pressure-bearing surface S′2 is arranged on a lower end surface, located in the balance chamber 1′4, of the valve core 3′1, the through hole 3′11 is required to be arranged on the valve core 3′1 to communicate the first connecting chamber 1′2 with the balance chamber 1′4 so as to realize equal pressures in the two chambers. On this basis, the guide ball 3′4 is required to be arranged at a lower end of the through hole of the valve core. To facilitate arranging the through hole 3′11 on the valve core 3′1, the transmission rod 3′2 and the valve body 3′1 are separated, and as a result, in the prior art, the valve core component has many parts including the transmission rod 3′2, the valve core 3′1 and the guide ball 3′4, which may cause a larger cumulative dimensional tolerance in an axial direction, a lowered adjusting precision of the valve and a troublesome assembly.
Secondly, the balance chamber 1′4 communicates with the first connecting chamber 1′2, and when the first connecting chamber 1′2 is a high pressure end, the balance chamber 1′4 has a high pressure, which requires a high sealing performance and increases a risk of leakage.
Thirdly, it is difficult to process the through hole 3′11 on the small valve core 3′1.
In view of this, a technical problem to be solved presently by those skilled in the art is to provide an improved thermal expansion valve, which may improve the reliability of sealing between a valve body and an upper end portion of the valve core component, improve the sensitivity of the valve, and reduce the difficulty for processing the valve body and the valve core component, and also may eliminate pressure influence on the movement of the valve core component caused by a refrigerant in a first connecting chamber.